Cutting rotor
BACKGROUND OF THE INVENTION 
     The present invention is related to a cutting rotor having blades clamped within grooves of the rotor body. 
     Such a rotor for the use in an extrusion granulator is known from the prospectus WIDIA-SCHNEIDROTOR of the Applicant, the blades being held in grooves one side wall of which is deformed by eccenters and pressed against one side of the blade portion engaging the groove. In this case, however, secure clamping of the blades is only achieved if the portion of the blade projecting into the groove, respectively the groove itself, is somewhat tapered towards the interior. Although this fixation is generally satisfactory, it has certain drawbacks. 
     It is also known to tighten the cutting blades to the rotor body by means of screws having conical heads (DE-A-2,120,491). In this case, only the direct screw forces can be used for the fixation. It is further known to fasten an insert tool by means of a screw having a conical head which acts onto an inclined surface of the insert tool by means of a rolling member (DE-A-3,511,580). However, this solution is expensive, space-consuming, and therefore not suitable for a cutting rotor. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to improve the clamping of the blade under simple manufacturing conditions. This object is attained, according to this invention, by the fact that each cutting blade is provided with at least one concave clamping surface against which a conical screw of a clamping element is applied. The axis of the conical screw is at least approximately parallel to the lengthwise direction of the cutting blade. The conical screw has a conical head which eccentrically abuts against said clamping surface. The clamping force thus has a radial and an axial component both acting upon the cutting blade. The said cone may now act onto the concave clamping surface in the radial and axial directions at the same time, whereby a secure, solid and precise clamping of the blade in any direction is achieved. It will be possible to adjust the axial position of the blade with precision within certain limits as well. In practice, there is no risk of soiling or sticking. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described in more detail by means of one embodiment and a variant thereof, with reference to the drawing wherein: 
     FIG. 1 is a partial front view of the cutting rotor, 
     FIG. 2 is a partly sectioned side view, and 
     FIG. 3 is a partial front view, corresponding to FIG. 1, of an alternative embodiment. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a small section of the circumference of the cutting rotor. Prismatic grooves 2 are milled into the circumference of the rotor body 1 with distances as small as e.g. 17 to 20 mm, each groove receiving a blade 3 having a cutting edge 4. On both front faces of the rotor, a clamping screw 5 is assigned to each blade 3, only their heads being visible in FIG. 1. As shown in FIG. 2, these clamping screws 5 which are fastened to the rotor body 1 are provided with a conical clamping surface 6 which cooperates with an adjoining concave clamping surface 7 on the blade 3. Thus, every blade 3 is provided at its both ends with a corresponding concave clamping surface 7 to which abuts the cone of a clamping screw 5. The clamping surfaces 7 may be cylindrical, whose inclination corresponds to the angle of inclination of the cone 6, so that each cone 6 is at rest on the clamping surface 7 along a generating line. As shown in FIG. 1, the conical surfaces 6 are slightly eccentric with reference to the clamping surfaces 7 of the blades 3 when they are mounted. It is contemplated in FIG. 1 that this contact generating line is situated e.g. in the left hand lateral surface of the blade 3, so that the clamping force F applied to the clamping surface 7 by the clamping cone 6 has about the direction represented in FIG. 1. When one of the conical screws 5 visible in FIG. 1 is tightened, the friction force applied by its conical surface 6 to the adjoining clamping surface 7 essentially acts radially inwards and supports the wedge effect in the desired sense. The conical screws on the opposite, rear face of the rotor have to be provided with left-hand threads in order to produce the same effect. This clamping force, however, has also a component in the lengthwise direction of the blade, i.e. in the axial direction of the blades 3, as indicated in FIG. 2. Thus, the blades are held in a definite position by the conical screws 5 since they are pressed, with their precision-machined surfaces, in the circumferential direction and, to the right as seen in FIG. 1, and also inwardly, against the groove walls and the groove bottom respectively. Additionally, they are axially secured because the conical screws prevent any axial displacement as well. The blades 3 are seated in the grooves 2 practically without any clearance, so that no dirt can penetrate into the rotor circumference. Therefore, it is virtually excluded that the clamping elements be soiled in any way that would impair the unclamping and dismounting of the blades for replacement. 
     The blades 3 are preferably made of a hard metal, in particular a hard metal with nickel or a nickel alloy such as nickel-chromium, nickel-molybdenum or nickel-titanium as a binder metal. The clamping surfaces 7 of the blades need not be of very high precision for it is not very critical in which direction the clamping force F exactly acts. However, it is important for the surfaces to be precise enough in order to guarantee a uniform mutual contact of the conical surfaces 6 with the clamping surfaces along a generating line so that no overstressing of the hard metal blade can occur. The precision of the clamping surfaces 7 obtained by sintering of the hard metal blades, however, is normally quite sufficient, i.e. finishing these clamping surfaces is not necessary. Therefore, the manufacture of the blades is not rendered substantially more expensive by the clamping surfaces 7, and furthermore, the shape of the blade is very simple, the long sides allowing a plane parallel grinding with a working overmeasure of e.g. 0.2 mm. A particular advantage of the represented embodiment consists in the possibility to precisely adjust the axial position of the blade by measured tightening of the two conical screws 6 assigned to each single blade 3. 
     In FIG. 3, which shows an alternative embodiment, corresponding parts are referenced as in FIG. 1. The difference is that in contrast to the embodiment according to FIG. 1, reversible blades 3&#39; are provided. They have a symmetrical cross section with two cutting edges 4. In this case, the grooves 2 have a different cross section, the groove bottom being inclined according to the flank of the blade. The groove 2 is provided with a recess 2a in the region of the inside cutting edge 4 of the blade 3&#39; in order to assure that the cutting edge 4 remains undamaged in any case. The reversible blade is provided on both ends 2 with symmetrical clamping surfaces 7. When the outside cutting edge 4 is worn, the blade 3&#39; may be removed, reversed, and inserted again.